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author | Karl Berry <karl@freefriends.org> | 2015-04-26 22:16:26 +0000 |
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committer | Karl Berry <karl@freefriends.org> | 2015-04-26 22:16:26 +0000 |
commit | 342e672574c4e67d510e46ab6acd0e21a7d0cf54 (patch) | |
tree | 79e04202d08c0404bbd780bd26c1e34710e539b6 /Master/tlpkg/tlperl/lib/version/Internals.pod | |
parent | be2706af7c57a0ef0f4d4e9f684ca4ef74922a82 (diff) |
(tl)perl 5.20.2 for windows, from siep
git-svn-id: svn://tug.org/texlive/trunk@37064 c570f23f-e606-0410-a88d-b1316a301751
Diffstat (limited to 'Master/tlpkg/tlperl/lib/version/Internals.pod')
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diff --git a/Master/tlpkg/tlperl/lib/version/Internals.pod b/Master/tlpkg/tlperl/lib/version/Internals.pod new file mode 100644 index 00000000000..95be8448811 --- /dev/null +++ b/Master/tlpkg/tlperl/lib/version/Internals.pod @@ -0,0 +1,699 @@ +=head1 NAME + +version::Internals - Perl extension for Version Objects + +=head1 DESCRIPTION + +Overloaded version objects for all modern versions of Perl. This documents +the internal data representation and underlying code for version.pm. See +F<version.pod> for daily usage. This document is only useful for users +interested in the gory details. + +=head1 WHAT IS A VERSION? + +For the purposes of this module, a version "number" is a sequence of +positive integer values separated by one or more decimal points and +optionally a single underscore. This corresponds to what Perl itself +uses for a version, as well as extending the "version as number" that +is discussed in the various editions of the Camel book. + +There are actually two distinct kinds of version objects: + +=over 4 + +=item Decimal Versions + +Any version which "looks like a number", see L<Decimal Versions>. This +also includes versions with a single decimal point and a single embedded +underscore, see L<Alpha Versions>, even though these must be quoted +to preserve the underscore formatting. + +=item Dotted-Decimal Versions + +Also referred to as "Dotted-Integer", these contains more than one decimal +point and may have an optional embedded underscore, see L<Dotted-Decimal +Versions>. This is what is commonly used in most open source software as +the "external" version (the one used as part of the tag or tarfile name). +A leading 'v' character is now required and will warn if it missing. + +=back + +Both of these methods will produce similar version objects, in that +the default stringification will yield the version L<Normal Form> only +if required: + + $v = version->new(1.002); # 1.002, but compares like 1.2.0 + $v = version->new(1.002003); # 1.002003 + $v2 = version->new("v1.2.3"); # v1.2.3 + +In specific, version numbers initialized as L<Decimal Versions> will +stringify as they were originally created (i.e. the same string that was +passed to C<new()>. Version numbers initialized as L<Dotted-Decimal Versions> +will be stringified as L<Normal Form>. + +=head2 Decimal Versions + +These correspond to historical versions of Perl itself prior to 5.6.0, +as well as all other modules which follow the Camel rules for the +$VERSION scalar. A Decimal version is initialized with what looks like +a floating point number. Leading zeros B<are> significant and trailing +zeros are implied so that a minimum of three places is maintained +between subversions. What this means is that any subversion (digits +to the right of the decimal place) that contains less than three digits +will have trailing zeros added to make up the difference, but only for +purposes of comparison with other version objects. For example: + + # Prints Equivalent to + $v = version->new( 1.2); # 1.2 v1.200.0 + $v = version->new( 1.02); # 1.02 v1.20.0 + $v = version->new( 1.002); # 1.002 v1.2.0 + $v = version->new( 1.0023); # 1.0023 v1.2.300 + $v = version->new( 1.00203); # 1.00203 v1.2.30 + $v = version->new( 1.002003); # 1.002003 v1.2.3 + +All of the preceding examples are true whether or not the input value is +quoted. The important feature is that the input value contains only a +single decimal. See also L<Alpha Versions>. + +IMPORTANT NOTE: As shown above, if your Decimal version contains more +than 3 significant digits after the decimal place, it will be split on +each multiple of 3, so 1.0003 is equivalent to v1.0.300, due to the need +to remain compatible with Perl's own 5.005_03 == 5.5.30 interpretation. +Any trailing zeros are ignored for mathematical comparison purposes. + +=head2 Dotted-Decimal Versions + +These are the newest form of versions, and correspond to Perl's own +version style beginning with 5.6.0. Starting with Perl 5.10.0, +and most likely Perl 6, this is likely to be the preferred form. This +method normally requires that the input parameter be quoted, although +Perl's after 5.8.1 can use v-strings as a special form of quoting, but +this is highly discouraged. + +Unlike L<Decimal Versions>, Dotted-Decimal Versions have more than +a single decimal point, e.g.: + + # Prints + $v = version->new( "v1.200"); # v1.200.0 + $v = version->new("v1.20.0"); # v1.20.0 + $v = qv("v1.2.3"); # v1.2.3 + $v = qv("1.2.3"); # v1.2.3 + $v = qv("1.20"); # v1.20.0 + +In general, Dotted-Decimal Versions permit the greatest amount of freedom +to specify a version, whereas Decimal Versions enforce a certain +uniformity. + +Just like L</Decimal Versions>, Dotted-Decimal Versions can be used as +L</Alpha Versions>. + +=head2 Alpha Versions + +For module authors using CPAN, the convention has been to note unstable +releases with an underscore in the version string. (See L<CPAN>.) version.pm +follows this convention and alpha releases will test as being newer than the +more recent stable release, and less than the next stable release. Only the +last element may be separated by an underscore: + + # Declaring + use version 0.77; our $VERSION = version->declare("v1.2_3"); + + # Parsing + $v1 = version->parse("v1.2_3"); + $v1 = version->parse("1.002_003"); + +Note that you B<must> quote the version when writing an alpha Decimal version. +The stringified form of Decimal versions will always be the same string that +was used to initialize the version object. + +=head2 Regular Expressions for Version Parsing + +A formalized definition of the legal forms for version strings is +included in the C<version::regex> class. Primitives are included for +common elements, although they are scoped to the file so they are useful +for reference purposes only. There are two publicly accessible scalars +that can be used in other code (not exported): + +=over 4 + +=item C<$version::LAX> + +This regexp covers all of the legal forms allowed under the current +version string parser. This is not to say that all of these forms +are recommended, and some of them can only be used when quoted. + +For dotted decimals: + + v1.2 + 1.2345.6 + v1.23_4 + +The leading 'v' is optional if two or more decimals appear. If only +a single decimal is included, then the leading 'v' is required to +trigger the dotted-decimal parsing. A leading zero is permitted, +though not recommended except when quoted, because of the risk that +Perl will treat the number as octal. A trailing underscore plus one +or more digits denotes an alpha or development release (and must be +quoted to be parsed properly). + +For decimal versions: + + 1 + 1.2345 + 1.2345_01 + +an integer portion, an optional decimal point, and optionally one or +more digits to the right of the decimal are all required. A trailing +underscore is permitted and a leading zero is permitted. Just like +the lax dotted-decimal version, quoting the values is required for +alpha/development forms to be parsed correctly. + +=item C<$version::STRICT> + +This regexp covers a much more limited set of formats and constitutes +the best practices for initializing version objects. Whether you choose +to employ decimal or dotted-decimal for is a personal preference however. + +=over 4 + +=item v1.234.5 + +For dotted-decimal versions, a leading 'v' is required, with three or +more sub-versions of no more than three digits. A leading 0 (zero) +before the first sub-version (in the above example, '1') is also +prohibited. + +=item 2.3456 + +For decimal versions, an integer portion (no leading 0), a decimal point, +and one or more digits to the right of the decimal are all required. + +=back + +=back + +Both of the provided scalars are already compiled as regular expressions +and do not contain either anchors or implicit groupings, so they can be +included in your own regular expressions freely. For example, consider +the following code: + + ($pkg, $ver) =~ / + ^[ \t]* + use [ \t]+($PKGNAME) + (?:[ \t]+($version::STRICT))? + [ \t]*; + /x; + +This would match a line of the form: + + use Foo::Bar::Baz v1.2.3; # legal only in Perl 5.8.1+ + +where C<$PKGNAME> is another regular expression that defines the legal +forms for package names. + +=head1 IMPLEMENTATION DETAILS + +=head2 Equivalence between Decimal and Dotted-Decimal Versions + +When Perl 5.6.0 was released, the decision was made to provide a +transformation between the old-style decimal versions and new-style +dotted-decimal versions: + + 5.6.0 == 5.006000 + 5.005_04 == 5.5.40 + +The floating point number is taken and split first on the single decimal +place, then each group of three digits to the right of the decimal makes up +the next digit, and so on until the number of significant digits is exhausted, +B<plus> enough trailing zeros to reach the next multiple of three. + +This was the method that version.pm adopted as well. Some examples may be +helpful: + + equivalent + decimal zero-padded dotted-decimal + ------- ----------- -------------- + 1.2 1.200 v1.200.0 + 1.02 1.020 v1.20.0 + 1.002 1.002 v1.2.0 + 1.0023 1.002300 v1.2.300 + 1.00203 1.002030 v1.2.30 + 1.002003 1.002003 v1.2.3 + +=head2 Quoting Rules + +Because of the nature of the Perl parsing and tokenizing routines, +certain initialization values B<must> be quoted in order to correctly +parse as the intended version, especially when using the C<declare> or +L</qv()> methods. While you do not have to quote decimal numbers when +creating version objects, it is always safe to quote B<all> initial values +when using version.pm methods, as this will ensure that what you type is +what is used. + +Additionally, if you quote your initializer, then the quoted value that goes +B<in> will be exactly what comes B<out> when your $VERSION is printed +(stringified). If you do not quote your value, Perl's normal numeric handling +comes into play and you may not get back what you were expecting. + +If you use a mathematic formula that resolves to a floating point number, +you are dependent on Perl's conversion routines to yield the version you +expect. You are pretty safe by dividing by a power of 10, for example, +but other operations are not likely to be what you intend. For example: + + $VERSION = version->new((qw$Revision: 1.4)[1]/10); + print $VERSION; # yields 0.14 + $V2 = version->new(100/9); # Integer overflow in decimal number + print $V2; # yields something like 11.111.111.100 + +Perl 5.8.1 and beyond are able to automatically quote v-strings but +that is not possible in earlier versions of Perl. In other words: + + $version = version->new("v2.5.4"); # legal in all versions of Perl + $newvers = version->new(v2.5.4); # legal only in Perl >= 5.8.1 + +=head2 What about v-strings? + +There are two ways to enter v-strings: a bare number with two or more +decimal points, or a bare number with one or more decimal points and a +leading 'v' character (also bare). For example: + + $vs1 = 1.2.3; # encoded as \1\2\3 + $vs2 = v1.2; # encoded as \1\2 + +However, the use of bare v-strings to initialize version objects is +B<strongly> discouraged in all circumstances. Also, bare +v-strings are not completely supported in any version of Perl prior to +5.8.1. + +If you insist on using bare v-strings with Perl > 5.6.0, be aware of the +following limitations: + +1) For Perl releases 5.6.0 through 5.8.0, the v-string code merely guesses, +based on some characteristics of v-strings. You B<must> use a three part +version, e.g. 1.2.3 or v1.2.3 in order for this heuristic to be successful. + +2) For Perl releases 5.8.1 and later, v-strings have changed in the Perl +core to be magical, which means that the version.pm code can automatically +determine whether the v-string encoding was used. + +3) In all cases, a version created using v-strings will have a stringified +form that has a leading 'v' character, for the simple reason that sometimes +it is impossible to tell whether one was present initially. + +=head2 Version Object Internals + +version.pm provides an overloaded version object that is designed to both +encapsulate the author's intended $VERSION assignment as well as make it +completely natural to use those objects as if they were numbers (e.g. for +comparisons). To do this, a version object contains both the original +representation as typed by the author, as well as a parsed representation +to ease comparisons. Version objects employ L<overload> methods to +simplify code that needs to compare, print, etc the objects. + +The internal structure of version objects is a blessed hash with several +components: + + bless( { + 'original' => 'v1.2.3_4', + 'alpha' => 1, + 'qv' => 1, + 'version' => [ + 1, + 2, + 3, + 4 + ] + }, 'version' ); + +=over 4 + +=item original + +A faithful representation of the value used to initialize this version +object. The only time this will not be precisely the same characters +that exist in the source file is if a short dotted-decimal version like +v1.2 was used (in which case it will contain 'v1.2'). This form is +B<STRONGLY> discouraged, in that it will confuse you and your users. + +=item qv + +A boolean that denotes whether this is a decimal or dotted-decimal version. +See L<version/is_qv()>. + +=item alpha + +A boolean that denotes whether this is an alpha version. NOTE: that the +underscore can only appear in the last position. See L<version/is_alpha()>. + +=item version + +An array of non-negative integers that is used for comparison purposes with +other version objects. + +=back + +=head2 Replacement UNIVERSAL::VERSION + +In addition to the version objects, this modules also replaces the core +UNIVERSAL::VERSION function with one that uses version objects for its +comparisons. The return from this operator is always the stringified form +as a simple scalar (i.e. not an object), but the warning message generated +includes either the stringified form or the normal form, depending on how +it was called. + +For example: + + package Foo; + $VERSION = 1.2; + + package Bar; + $VERSION = "v1.3.5"; # works with all Perl's (since it is quoted) + + package main; + use version; + + print $Foo::VERSION; # prints 1.2 + + print $Bar::VERSION; # prints 1.003005 + + eval "use foo 10"; + print $@; # prints "foo version 10 required..." + eval "use foo 1.3.5; # work in Perl 5.6.1 or better + print $@; # prints "foo version 1.3.5 required..." + + eval "use bar 1.3.6"; + print $@; # prints "bar version 1.3.6 required..." + eval "use bar 1.004"; # note Decimal version + print $@; # prints "bar version 1.004 required..." + + +IMPORTANT NOTE: This may mean that code which searches for a specific +string (to determine whether a given module is available) may need to be +changed. It is always better to use the built-in comparison implicit in +C<use> or C<require>, rather than manually poking at C<< class->VERSION >> +and then doing a comparison yourself. + +The replacement UNIVERSAL::VERSION, when used as a function, like this: + + print $module->VERSION; + +will also exclusively return the stringified form. See L</Stringification> +for more details. + +=head1 USAGE DETAILS + +=head2 Using modules that use version.pm + +As much as possible, the version.pm module remains compatible with all +current code. However, if your module is using a module that has defined +C<$VERSION> using the version class, there are a couple of things to be +aware of. For purposes of discussion, we will assume that we have the +following module installed: + + package Example; + use version; $VERSION = qv('1.2.2'); + ...module code here... + 1; + +=over 4 + +=item Decimal versions always work + +Code of the form: + + use Example 1.002003; + +will always work correctly. The C<use> will perform an automatic +C<$VERSION> comparison using the floating point number given as the first +term after the module name (e.g. above 1.002.003). In this case, the +installed module is too old for the requested line, so you would see an +error like: + + Example version 1.002003 (v1.2.3) required--this is only version 1.002002 (v1.2.2)... + +=item Dotted-Decimal version work sometimes + +With Perl >= 5.6.2, you can also use a line like this: + + use Example 1.2.3; + +and it will again work (i.e. give the error message as above), even with +releases of Perl which do not normally support v-strings (see L<What about v-strings?> above). This has to do with that fact that C<use> only checks +to see if the second term I<looks like a number> and passes that to the +replacement L<UNIVERSAL::VERSION|UNIVERSAL/VERSION>. This is not true in Perl 5.005_04, +however, so you are B<strongly encouraged> to always use a Decimal version +in your code, even for those versions of Perl which support the Dotted-Decimal +version. + +=back + +=head2 Object Methods + +=over 4 + +=item new() + +Like many OO interfaces, the new() method is used to initialize version +objects. If two arguments are passed to C<new()>, the B<second> one will be +used as if it were prefixed with "v". This is to support historical use of the +C<qw> operator with the CVS variable $Revision, which is automatically +incremented by CVS every time the file is committed to the repository. + +In order to facilitate this feature, the following +code can be employed: + + $VERSION = version->new(qw$Revision: 2.7 $); + +and the version object will be created as if the following code +were used: + + $VERSION = version->new("v2.7"); + +In other words, the version will be automatically parsed out of the +string, and it will be quoted to preserve the meaning CVS normally +carries for versions. The CVS $Revision$ increments differently from +Decimal versions (i.e. 1.10 follows 1.9), so it must be handled as if +it were a Dotted-Decimal Version. + +A new version object can be created as a copy of an existing version +object, either as a class method: + + $v1 = version->new(12.3); + $v2 = version->new($v1); + +or as an object method: + + $v1 = version->new(12.3); + $v2 = $v1->new(12.3); + +and in each case, $v1 and $v2 will be identical. NOTE: if you create +a new object using an existing object like this: + + $v2 = $v1->new(); + +the new object B<will not> be a clone of the existing object. In the +example case, $v2 will be an empty object of the same type as $v1. + +=back + +=over 4 + +=item qv() + +An alternate way to create a new version object is through the exported +qv() sub. This is not strictly like other q? operators (like qq, qw), +in that the only delimiters supported are parentheses (or spaces). It is +the best way to initialize a short version without triggering the floating +point interpretation. For example: + + $v1 = qv(1.2); # v1.2.0 + $v2 = qv("1.2"); # also v1.2.0 + +As you can see, either a bare number or a quoted string can usually +be used interchangeably, except in the case of a trailing zero, which +must be quoted to be converted properly. For this reason, it is strongly +recommended that all initializers to qv() be quoted strings instead of +bare numbers. + +To prevent the C<qv()> function from being exported to the caller's namespace, +either use version with a null parameter: + + use version (); + +or just require version, like this: + + require version; + +Both methods will prevent the import() method from firing and exporting the +C<qv()> sub. + +=back + +For the subsequent examples, the following three objects will be used: + + $ver = version->new("1.2.3.4"); # see "Quoting Rules" + $alpha = version->new("1.2.3_4"); # see "Alpha Versions" + $nver = version->new(1.002); # see "Decimal Versions" + +=over 4 + +=item Normal Form + +For any version object which is initialized with multiple decimal +places (either quoted or if possible v-string), or initialized using +the L<qv()|version/qv()> operator, the stringified representation is returned in +a normalized or reduced form (no extraneous zeros), and with a leading 'v': + + print $ver->normal; # prints as v1.2.3.4 + print $ver->stringify; # ditto + print $ver; # ditto + print $nver->normal; # prints as v1.2.0 + print $nver->stringify; # prints as 1.002, + # see "Stringification" + +In order to preserve the meaning of the processed version, the +normalized representation will always contain at least three sub terms. +In other words, the following is guaranteed to always be true: + + my $newver = version->new($ver->stringify); + if ($newver eq $ver ) # always true + {...} + +=back + +=over 4 + +=item Numification + +Although all mathematical operations on version objects are forbidden +by default, it is possible to retrieve a number which corresponds +to the version object through the use of the $obj->numify +method. For formatting purposes, when displaying a number which +corresponds a version object, all sub versions are assumed to have +three decimal places. So for example: + + print $ver->numify; # prints 1.002003004 + print $nver->numify; # prints 1.002 + +Unlike the stringification operator, there is never any need to append +trailing zeros to preserve the correct version value. + +=back + +=over 4 + +=item Stringification + +The default stringification for version objects returns exactly the same +string as was used to create it, whether you used C<new()> or C<qv()>, +with one exception. The sole exception is if the object was created using +C<qv()> and the initializer did not have two decimal places or a leading +'v' (both optional), then the stringified form will have a leading 'v' +prepended, in order to support round-trip processing. + +For example: + + Initialized as Stringifies to + ============== ============== + version->new("1.2") 1.2 + version->new("v1.2") v1.2 + qv("1.2.3") 1.2.3 + qv("v1.3.5") v1.3.5 + qv("1.2") v1.2 ### exceptional case + +See also L<UNIVERSAL::VERSION|UNIVERSAL/VERSION>, as this also returns the stringified form +when used as a class method. + +IMPORTANT NOTE: There is one exceptional cases shown in the above table +where the "initializer" is not stringwise equivalent to the stringified +representation. If you use the C<qv>() operator on a version without a +leading 'v' B<and> with only a single decimal place, the stringified output +will have a leading 'v', to preserve the sense. See the L</qv()> operator +for more details. + +IMPORTANT NOTE 2: Attempting to bypass the normal stringification rules by +manually applying L<numify()|version/numify()> and L<normal()|version/normal()> will sometimes yield +surprising results: + + print version->new(version->new("v1.0")->numify)->normal; # v1.0.0 + +The reason for this is that the L<numify()|version/numify()> operator will turn "v1.0" +into the equivalent string "1.000000". Forcing the outer version object +to L<normal()|version/normal()> form will display the mathematically equivalent "v1.0.0". + +As the example in L</new()> shows, you can always create a copy of an +existing version object with the same value by the very compact: + + $v2 = $v1->new($v1); + +and be assured that both C<$v1> and C<$v2> will be completely equivalent, +down to the same internal representation as well as stringification. + +=back + +=over 4 + +=item Comparison operators + +Both C<cmp> and C<E<lt>=E<gt>> operators perform the same comparison between +terms (upgrading to a version object automatically). Perl automatically +generates all of the other comparison operators based on those two. +In addition to the obvious equalities listed below, appending a single +trailing 0 term does not change the value of a version for comparison +purposes. In other words "v1.2" and "1.2.0" will compare as identical. + +For example, the following relations hold: + + As Number As String Truth Value + ------------- ---------------- ----------- + $ver > 1.0 $ver gt "1.0" true + $ver < 2.5 $ver lt true + $ver != 1.3 $ver ne "1.3" true + $ver == 1.2 $ver eq "1.2" false + $ver == 1.2.3.4 $ver eq "1.2.3.4" see discussion below + +It is probably best to chose either the Decimal notation or the string +notation and stick with it, to reduce confusion. Perl6 version objects +B<may> only support Decimal comparisons. See also L<Quoting Rules>. + +WARNING: Comparing version with unequal numbers of decimal points (whether +explicitly or implicitly initialized), may yield unexpected results at +first glance. For example, the following inequalities hold: + + version->new(0.96) > version->new(0.95); # 0.960.0 > 0.950.0 + version->new("0.96.1") < version->new(0.95); # 0.096.1 < 0.950.0 + +For this reason, it is best to use either exclusively L<Decimal Versions> or +L<Dotted-Decimal Versions> with multiple decimal points. + +=back + +=over 4 + +=item Logical Operators + +If you need to test whether a version object +has been initialized, you can simply test it directly: + + $vobj = version->new($something); + if ( $vobj ) # true only if $something was non-blank + +You can also test whether a version object is an alpha version, for +example to prevent the use of some feature not present in the main +release: + + $vobj = version->new("1.2_3"); # MUST QUOTE + ...later... + if ( $vobj->is_alpha ) # True + +=back + +=head1 AUTHOR + +John Peacock E<lt>jpeacock@cpan.orgE<gt> + +=head1 SEE ALSO + +L<perl>. + +=cut |